The present invention relates generally to the field of electrical insulating systems. More particularly, the invention relates to a novel technique for insulating conductors, such as windings in electric motors and similar machines.
Many applications exist for electrical conductors and insulating systems for such conductors. Insulating systems typically vary widely in configuration and application, depending upon such factors as the voltage levels of the applications, anticipated current loads, constraints and concerns regarding installation, and so forth. In insulating systems for conductors such as those found in windings of electric motors, generators, dynamos, and similar machines, both manual and semi-automated insulation techniques have been proposed and are presently in use.
In electric motor winding environments, for example, conductors are electrically insulated from one another, typically at ends of a stator or rotor. Where possible, pre-assembled or prefabricated insulators may be applied to the conductors, such as in the form of sleeves or bonded tape. Where higher voltage ratings are needed, multiple layers of the insulators may be employed. The layers typically include resin disposed between the multiple layers, rendering the sleeves relatively stiff and resistant to bending. While such stiffness may not pose significant problems for certain applications, other applications, particularly for larger conductors, result in breakage, cracking, and other degradation of the insulation sleeves.
In many applications, the degradation of insulation can lead to significant drawbacks and even premature damage or failure of the associated conductors and machine. In general, it is advantageous to provide the optimal dielectric path between the conductor and surrounding conductors to optimize the insulation capabilities. However, where cracks or breaks occur in the insulating sleeves, new paths are defined which will typically be less optimal then the original paths provided by the insulating material.
In addition to the foregoing drawbacks, conventional insulating systems may require expensive hand taping, or costly materials. Known insulating sleeves such as mylar, aramid fibers, silicon and acrylics, for example, are used only to limited satisfaction. Acrylics, for example, can be expensive and may not be suitable for higher voltages. Silicone sleeves suffer from drawbacks including a limited ability to provide sealing against water penetration.
There is, therefore, a need at present for an improved insulating system for conductors which addresses such drawbacks. There is, at present, a particular need for an insulating system which can be adapted for a variety of voltage ratings and conductor sizes, while providing flexibility during the assembly process to avoid cracking or breaking of the insulation material.
The present invention provides an insulating system designed to respond to such needs. The system may be used in a wide variety of settings, and is particularly well-suited to insulation of conductors in environments such as electric motors, generators, dynamos, and other electrical machines. The technique can be adapted for a range of voltage ratings and conductor sizes. The technique also avoids or limits the potential for cracking or breaking of insulating sleeves as they are applied to conductors, and may eliminate the need for hand taping in higher voltage applications such as electric motors.
In accordance with certain aspects of the technique, multi-layer insulating sleeves or tubes are developed in which a tape or similar insulating material is wound on a mandrel. The layers of insulating material may be xe2x80x9cbutt lappedxe2x80x9d or provided with zero percent overlap, while other layers within the tubes may include some degree of overlap. The tubes may be formed in a series or family, permitting multiple tubes to be prefabricated and selected depending upon the overall voltage rating of the insulation. Tubes in the series may be nested or slid within one another to provide the desired rating. While the layers of the tubes are bonded to one another, tubes in the system are not bonded to one another during installation. Rather, the tubes are installed on a conductor while permitting mutual displacement of one tube with respect to another to avoid damage, cracking or breakage of the various tubes. Following installation on the conductor, the tubes may be bonded to one another and to the conductor.
Where a family of tubes are provided in a system, adjacent sizes of tubes may include windings in opposite directions. Thus, dielectric paths through the resulting nested tubes are optimized and maximized to enhance the insulation capabilities of the overall assembly.
The construction of the individual tubes may follow right-hand helical winding or left-hand helical winding. Various layers of the tube may be wound in the same helical direction, or may be wound in opposite helical directions. Again, however, when the overall system is assembled with two or more tubes, at least some layers of the system preferably include oppositely-wound tape. Once the system is prefabricated, the present technique provides for cutting, assembly, installation and bonding of the insulation tubes to the conductor for final processing of the conductor and machine.